I never used the word "casual" in relation to gaming. "Casual gaming" is a pleonasm anyway.
I used "hardcore" a few times, but I always made sure the sarcasm is apparent and what I really mean is "retarded teenagers with too much time on their hands playing nothing but piss-easy M-rated 3D games". I don't believe a valid definition exists for this one either.
In general, I tend to disregard anything said by people who use those terms seriously.